The present invention relates to controlling foaming in paper and pulp mills. The present invention further relates to defoamer compositions that can be used to treat pulp or black liquor in pulp processing, or used to treat process waters in pulp and paper making processes.
In various steps of pulping and paper making, the creation of unwanted foam can occur. This generally occurs due to the various chemicals used in the pulp and paper making processes. One particular area that faces undesirable foam formation is in the pulp washing stage where wash water is used to wash the pulp and remove pulping chemicals and lignin. Previous defoaming technology, especially for pulp washing or brown stock washing stages, involved the use of petroleum based products such as hydrocarbon based oils, high melting point waxes, and one or more components that are treated with silicone oil. While these defoamer compositions have been considered effective in the controlling of foam, certain pulp and paper manufacturers wish to greatly avoid the presence of waxes and/or silicone oils since typically a residual of these chemicals cannot be removed from the pulp and upon testing are found to be present in the pulp. Specifically, the addition of oil based types of defoamers can cause a negative impact and/or an increase in pitch or dirt deposits in the paper making and pulp processing stages. For instance, these deposits can contain large amounts of high molecular weight fractions of oils and insoluble amide waxes which can cause fouling of wires, felts, and other components in subsequent paper making operations. Also, if the silicone components that are in the defoamer are not properly dispersed into the black liquor system and therefore not washed out during the washing process, this can have a negative effect on the final paper sheet that is made and any silicone carryover onto the paper products can affect the overall quality of the pulp and eventually the paper product thus downgrading the quality of the product.
Accordingly, there is a need in the paper making and pulp processing industry to develop defoamer compositions which are preferably free of silicone oil and/or free of high molecular weight wax and yet still achieve comparable defoaming activity in the paper and pulp mill.